1. Field of the Invention
The present invention relates to multilayered structures having neat appearance and excellent gas barrier properties.
2. Description of the Prior Art
Multilayered plastic packaging materials comprising a layer of a thermoplastic resin, particularly a polyolefin, having excellent mechanical properties and resistance to moisture, and, via an adhesive resin, a layer of a saponified product of an ethylene-vinyl acetate copolymer (hereinafter referred to as EVOH) are widely used, as oxygen-barrier containers, for packaging foods, cosmetics, pharmaceuticals, chemicals, toilettery and the like.
When these multilayered plastic containers are produced, what is known as "regrind" necessarily generates, such as fins caused by pinch-off in blow molding of bottles and punched wastes in molding cups, and their reuse is required from the viewpoint of economy and resource-saving. To effectively reuse the regrind, Japanese Patent Publication No. 29409/1984 discloses a process which comprises mixing the regrind into a thermoplastic resin layer such as polyolefin, which is principal raw material, and Japanese Patent Application Laid-open No. 101338/1984 discloses a process which comprises interposing the regrind between a thermoplastic resin layer and an EVOH layer. However, when most of thermoplastic resins, particularly polyolefin is melt extrusion molded simultaneously with scrap resins containing EVOH, the EVOH tends to deteriorate to cause black deposits ("charred resin on screw") to generate inside the extruder, or gelled matters ("lip stain") to adhere to dielip and other parts, and further nonuniform phase-separated irregular matters or abnormal flow to generate. These troubles then impair the properties of molded articles, such as deterioration of appearance, that of odor-keeping properties due to smell of decomposed resins and decrease in mechanical properties including resistance to shock. Accordingly, this type of extrusion molding cannot be practiced at all, or, is, if ever, practiced in most cases only for a short period of time.
Furthermore, when EVOH is co-extrusion molded together with a blend of polyolefin and EVOH, the molded articles tend to have turbulence (wavy pattern) on their surface and suffer delamination.